1. Field of the Invention
The present invention relates to a material or structure that resists ballistic penetration and mechanical impact forces. More specifically, the present invention relates to a material that is comprised of a matrix of polymeric fibers in which a plurality of microspheres are spread throughout.
2. Description of the Related Art
The invention of linear polyamides (e.g., nylon, nylon 6, etc.), has lead to further research for new synthetic textile fibers, polyester fibers, polyurethane fibers, etc. This research led to the invention of a type of fibers which have high heat resistance and high resistance to mechanical strain. These new fibers are classified under the generic name of "para amide fibers" (or simply aramid fibers), and include KEVLAR.RTM., NOMEX.RTM. and TWARON.RTM., three important members of this group.
Aramid polymers are a product of the reaction of the amino groups of a p-diaminobenzene compound and the acid groups of a terephthalic acid compound. (The first example of a para amide polymer in this series was obtained from the polymerization of p-aminobenzoic acid, coded PPD-T.)
In view of its superior mechanical and dynamic properties, its reduced expansion and thermal conductivity, its excellent abrasion resistance, heat resistance and chemical inertia, the aramid fibers and in particular, KEVLAR.RTM. and TWARON.RTM. have been used in a great number of applications in the manufacture of ropes, laminated tissues, etc. Aramid fibers are also used in the field of ballistic protection, both as soft body armors and heavy, high coverage armors, instead of body armors and bullet-resistant vests that are made of, for example, polyester fibers or nylon fibers.
The application of polymeric fiber materials in ballistic protection replaced other integrated structures with denser materials such as glass fibers or aluminum fibers. The ballistic resistance of polymeric fibers is greater than that of glass or aluminum fibers. It is believed that the ballistic resistance of fibers in general is due to the fact that, as a consequence of the impact and the penetration of the bullets, the yarns are stretched and thus absorb the energy of the projectile and dissipate that energy laterally (through the fibrous yarns which surround the impact zone) and also dissipate that energy longitudinally in the direction of the projectile. Aramids, the same as their predecessors, aliphatic polyamides and polyesters, are used under the form of flexible structures (of woven fibers arranged in juxtaposed layers or of masses of felt-like (i.e., unwoven) fibers having the thickness determined by the degree of exposure to projectiles) or rigid structures of laminate aramids for fragment and bullet-resistant garments and body armor panels. These structures and pieces are applicable for both soft armors and heavy armors.
Materials used in ballistic protection should meet the regulations of standard norms, which vary in each country. The standard norms establish the conditions to measure the speed of projectiles, and to measure penetration of the projectile into the material to determine the limit of the material. Ballistic resistance, for example, is the maximum velocity at which a fired bullet may be stopped and the bullet resistance corresponds to a "V.sub.50 " value, which is defined as the velocity at which the penetration probability is 50%.
Another factor contemplated by the norms refers to the body protection and is important for the design and manufacture of personal body armors and garments. The body protection is the magnitude and the profile of the deformation in the armor backing material or support of a bullet defense. This deformation, which for a certain defense, depends on the caliber, the weight, the velocity and the kind of bullet or fragment, may cause damage or bodily injuries, the severity of which also depends on the point of impact, since part of the energy of each impact is felt and received in the area of the body which is in line with the point of impact and results in traumas of a particularly severe nature when they correspond to the hepatic region, the left iliac cavity, the spine, etc. The maximum deformation of the rear part of a ballistic defense after the impact is called "trauma", and is quantitatively expressed by its depth (the length of the deformation in the direction of the impact).
In practice, the ballistic protection (soft or rigid) is obtained by panels (also called packets) that are formed by a layer or a plurality of layers of fabrics made of woven or felt-like (i.e., unwoven) aramid fibers, such as KEVLAR 29.RTM., KEVLAR 49.RTM., TWARON CT 930.RTM., TWARON 1260.RTM., etc. Each panel is covered by a hermetic, waterproof, flexible cover or envelope having a predetermined thickness and design depending on the level of protection desired and the bullet parameters. Depending on each case, the flexible cover may be backstitched in order to increase the density of the fiber mass.
In laminated materials, the woven or unwoven aramid fibers are combined with polyester resins, phenolic resins, elastomers, and depending on each case, with carbon fibers or ceramic fibers to form a structure to be applied in heavy ballistic armors (e.g., helmets, defensive armors for vehicles, shelters or cabins, etc.)
Trauma may be controlled by modifying the thickness of the ballistic panels, the density of the fiber mass, the weave pattern of the fibers, etc. Additionally, trauma may be controlled by incorporating additional laminates of antitrauma packets, aramid fillings or ceramic plates which cover the whole or a part of the front or the back of the ballistic panels.